It's not the first time that Clarkson & Co. have whipped out their iPhones, but last night the Top Gear team used the Apple handset twice over in their feature on the grand tourer super cars.

Bluetooth

The first tech trial for the three TV motor journos was to pair their mobiles with their in-car stereos. Mercifully, the iPhone plugged that particular spec gap nearly 2 years ago now but, sadly, Richard Hammond's Ferrari voice activation seemed to have a mind of its own - just in case that's the kind of thing that might put you off buying a Ferrari California. While you're at it, you might want to check that the pattern of the tyre treads is pretty enough for you too.

Satnavs

The next tech test for the cars was with their in-built satnav's. Both the Ferrari's system and the Aston Martin's seemed to work just fine despite Clarkson's initial concern with the Volvo model featured in the latter of the two vehicles. However, there were some issues with the Audi-built unit in James May's Lamborghini which didn't seem to recognise the existence of Romania whatsoever. Another thing to look out for if you're in that small subset of people who both own one of these luxury vehicles and also happens to be holidaying in Bucharest too.

Decibel iPhone app

The star of the show though, and the one you'll only need 59p/99c to road test, is the sound measuring app called, simply enough, Decibel. Currently in version 1.2, the 0.2MB app measures noise levels through the iPhone microphone and displays the readings both as a digital counter and an analogue needle. The three separate figures show the current decibel count, the maximum reading since recording began and the peak which is more of a current indicator of the maximum.

It is available for both the iPod touch and the iPhone, but beware that the touch has no built-in microphone, so you'll need a headset of some sort to get a reading with it. Another thing to look out for is that the iPhone mic clips at 100-105 decibels, meaning you're not going to be able to measure any sounds above a loud shout, so you can forget about trying it out at gigs.

That said, one use apart from measuring the sound of a super car's engine in an ex-Romanian dictator's secret network of underground road tunnels, might be if you happen to be complaining to your local council or constabulary about some noisy neighbours. They'll often ask for a measurement and it'll save the tedium of them having to send round a team to record it, by which time next door's banging might well have stopped. Perhaps not the cheeriest of uses but a use nonetheless.

Since its release, Decibel has been one of the top paid apps across Europe and doubtless Tomas Matuschek, the Swedish software architect behind the product, will be rather happy to note a slightly bigger cheque from Apple this month. If you want to give it a go on your iPhone, then you can find Decibel, as featured on Top Gear, here.